DBIO Dissertation Award Emergent behaviors in complex microbial ecosystems

From tropical forests to gut microbiomes, ecological communities harbor diverse and abundant species. Understanding the complex emergent phenomena of diversity, stability, and invasibility in these communities within a unified framework has been a significant challenge. We address this knowledge gap by bridging experiment and theory showing that simple community-level features govern emergent behaviors. As the number of species or the strength of interactions increases, microbial ecosystems transition through three distinct dynamical phases: from stable coexistence to partial coexistence, to the emergence of persistent fluctuations and alternative stable states in species abundances. Notably, high biodiversity and dynamic fluctuations reinforce each other. Furthermore, we show that the interplay between dynamics, interaction strength, and diversity determines the invasion outcome in microbial communities. Communities with fluctuations in species abundance are both more invasible and more diverse than stable communities, leading to a positive diversity-invasibility relationship. Increasing interspecies interaction strength and species pool size leads to a decrease in invasion probability. We resolve the diversity-invasibility debate by showing a universal positive correspondence between invasibility and survival fraction of resident species. Communities composed of strongly interacting species can exhibit an emergent priority effect in which invader species are less likely to colonize than species in the original pool. Overall, my work uncovers predictable emergent patterns of diversity, dynamics, and invasibility in ecological communities, offering insights into a unified framework for microbial ecology.